Refactor stack growth to be helper functions in exception for easier merging

.gitlab-ci.yml

@@ -37,4 +37,4 @@ test_vm:
   extends: .pintos_tests
   variables:
     DIR: vm
-    IGNORE: (tests/vm/pt-overflowstk|tests/vm/page-linear|tests/vm/page-parallel|tests/vm/page-merge-seq|tests/vm/page-merge-par|tests/vm/page-merge-stk|tests/vm/page-merge-mm|tests/vm/mmap-read|tests/vm/mmap-close|tests/vm/mmap-overlap|tests/vm/mmap-twice|tests/vm/mmap-write|tests/vm/mmap-exit|tests/vm/mmap-shuffle|tests/vm/mmap-clean|tests/vm/mmap-inherit|tests/vm/mmap-misalign|tests/vm/mmap-null|tests/vm/mmap-over-code|tests/vm/mmap-over-data|tests/vm/mmap-over-stk|tests/vm/mmap-remove)
+    IGNORE: (tests/vm/pt-grow-stack|tests/vm/pt-grow-pusha|tests/vm/pt-big-stk-obj|tests/vm/pt-overflowstk|tests/vm/pt-write-code2|tests/vm/pt-grow-stk-sc|tests/vm/page-linear|tests/vm/page-parallel|tests/vm/page-merge-seq|tests/vm/page-merge-par|tests/vm/page-merge-stk|tests/vm/page-merge-mm|tests/vm/mmap-read|tests/vm/mmap-close|tests/vm/mmap-overlap|tests/vm/mmap-twice|tests/vm/mmap-write|tests/vm/mmap-exit|tests/vm/mmap-shuffle|tests/vm/mmap-clean|tests/vm/mmap-inherit|tests/vm/mmap-misalign|tests/vm/mmap-null|tests/vm/mmap-over-code|tests/vm/mmap-over-data|tests/vm/mmap-over-stk|tests/vm/mmap-remove)

src/Makefile.build

@@ -65,7 +65,6 @@ userprog_SRC += userprog/tss.c		# TSS management.
 vm_SRC += vm/frame.c                    # Frame table manager.
 vm_SRC += vm/page.c                     # Page table manager.
 vm_SRC += devices/swap.c		# Swap block manager.
-vm_SRC += vm/stackgrowth.c              # Stack growth functions.
 #vm_SRC = vm/file.c			# Some other file.
 
 # Filesystem code.

src/userprog/Make.vars

@@ -1,7 +1,7 @@
 # -*- makefile -*-
 
-kernel.bin: DEFINES = -DUSERPROG -DFILESYS
-KERNEL_SUBDIRS = threads devices lib lib/kernel userprog filesys
+kernel.bin: DEFINES = -DUSERPROG -DFILESYS -DVM
+KERNEL_SUBDIRS = threads devices lib lib/kernel userprog filesys vm
 TEST_SUBDIRS = tests/userprog tests/userprog/no-vm tests/filesys/base
 GRADING_FILE = $(SRCDIR)/tests/userprog/Grading
 SIMULATOR = --qemu

src/userprog/exception.c

@@ -2,9 +2,15 @@
 #include <inttypes.h>
 #include <stdio.h>
 #include "userprog/gdt.h"
+#include "userprog/pagedir.h"
+#include "userprog/process.h"
 #include "threads/interrupt.h"
+#include "threads/palloc.h"
 #include "threads/thread.h"
-#include "vm/stackgrowth.h"
+#include "threads/vaddr.h"
+
+#define MAX_STACK_SIZE (8 * 1024 * 1024) // 8MB
+#define MAX_STACK_OFFSET 32 // 32 bytes offset below stack pointer (ESP)
 
 /* Number of page faults processed. */
 static long long page_fault_cnt;
@@ -12,6 +18,9 @@ static long long page_fault_cnt;
 static void kill (struct intr_frame *);
 static void page_fault (struct intr_frame *);
 
+static bool is_valid_stack_access (const void *fault_addr, const void *esp);
+static bool grow_stack (void *upage);
+
 /* Registers handlers for interrupts that can be caused by user
    programs.
 
@@ -146,18 +155,26 @@ page_fault (struct intr_frame *f)
   write = (f->error_code & PF_W) != 0;
   user = (f->error_code & PF_U) != 0;
 
-#ifdef VM
-  if (user && not_present)
+  if (!user || !not_present)
+  {
+    f->eip = (void *)f->eax;
+    f->eax = 0xffffffff;
+    return;
+  }
+
+  /* If the fault address is in a user page that is not present, then it might
+   be just that the stack needs to grow. So we attempt to grow the stack. */
+  void *upage = pg_round_down (fault_addr);
+  if (not_present && is_user_vaddr (upage) && upage != NULL)
     {
-      if (handle_stack_fault (fault_addr, f->esp)) return;
+      if (is_valid_stack_access (fault_addr, f->esp))
+        {
+          if (grow_stack (upage))
+            return;
+        }
+
+      /* TODO: Check SPT for the page. */
     }
-  else
-    {
-      f->eip = (void *)f->eax;
-      f->eax = 0xffffffff;
-      return;
-    }
-#endif
 
   /* To implement virtual memory, delete the rest of the function
      body, and replace it with code that brings in the page to
@@ -170,3 +187,50 @@ page_fault (struct intr_frame *f)
   kill (f);
 }
 
+/* Validates whether the fault address is a valid stack access. Access is a
+   valid stack access under the following two conditions:
+     1. The fault address must be within MAX_STACK_OFFSET (32) bytes below
+      the current stack pointer. (Accounts for both PUSH and PUSHA instructions)
+     2. Growing this stack to this address does not cause it to exceed the
+      MAX_STACK_SIZE (8MB) limit.
+
+   Returns true if both conditions are met, false otherwise.
+
+   Pre: fault_addr is a valid user virtual address (so also not NULL). */
+static bool
+is_valid_stack_access (const void *fault_addr, const void *esp)
+{
+  uint32_t new_stack_size = PHYS_BASE - pg_round_down (fault_addr);
+
+  uint32_t *lowest_valid_push_addr = (uint32_t *)esp - MAX_STACK_OFFSET;
+  bool is_within_push_range = (uint32_t *)fault_addr >= lowest_valid_push_addr;
+
+  return is_within_push_range && new_stack_size <= MAX_STACK_SIZE;
+}
+
+/* Attempts to grow the stack by allocating and mapping a new page.
+  This involves:
+    1. Allocating a zeroed page from the user pool
+    2. Installing it into the page table with write permissions
+
+  Returns true if the stack was successfully grown, false if either
+  allocation or installation fails.
+
+  Pre: upage is a valid page-aligned address (so also not NULL). */
+static bool
+grow_stack (void *upage)
+{
+  /* Allocate new page for stack */
+  void *kpage = palloc_get_page (PAL_USER | PAL_ZERO);
+  if (kpage == NULL)
+    return false;
+
+  /* Install the page into user page table */
+  if (!install_page (upage, kpage, true))
+    {
+      palloc_free_page (kpage);
+      return false;
+    }
+
+  return true;
+}

src/userprog/pagedir.c

@@ -53,7 +53,7 @@ pagedir_destroy (uint32_t *pd)
    on CREATE.  If CREATE is true, then a new page table is
    created and a pointer into it is returned.  Otherwise, a null
    pointer is returned. */
-uint32_t *
+static uint32_t *
 lookup_page (uint32_t *pd, const void *vaddr, bool create)
 {
   uint32_t *pt, *pde;

src/userprog/pagedir.h

@@ -6,7 +6,6 @@
 
 uint32_t *pagedir_create (void);
 void pagedir_destroy (uint32_t *pd);
-uint32_t *lookup_page (uint32_t *pd, const void *vaddr, bool create);
 bool pagedir_set_page (uint32_t *pd, void *upage, void *kpage, bool rw);
 void *pagedir_get_page (uint32_t *pd, const void *upage);
 void pagedir_clear_page (uint32_t *pd, void *upage);

src/userprog/process.c

@@ -118,7 +118,7 @@ process_execute (const char *cmd)
 
 static void *get_usr_kpage (enum palloc_flags flags, void *upage);
 static void free_usr_kpage (void *kpage);
-static bool install_page (void *upage, void *kpage, bool writable);
+bool install_page (void *upage, void *kpage, bool writable);
 
 static bool process_init_stack (char *cmd_saveptr, void **esp, char *file_name);
 static void *push_to_stack (void **esp, void *data, size_t data_size);
@@ -809,7 +809,7 @@ free_usr_kpage (void *kpage)
    with palloc_get_page().
    Returns true on success, false if UPAGE is already mapped or
    if memory allocation fails. */
-static bool
+bool
 install_page (void *upage, void *kpage, bool writable)
 {
   struct thread *t = thread_current ();

src/userprog/process.h

@@ -8,4 +8,6 @@ int process_wait (tid_t);
 void process_exit (void);
 void process_activate (void);
 
+bool install_page (void *upage, void *kpage, bool writable);
+
 #endif /* userprog/process.h */

src/vm/page.c

@@ -1,9 +1,4 @@
 #include "page.h"
-#include "userprog/pagedir.h"
-#include "threads/pte.h"
-
-#define SWAP_FLAG_BIT 9
-#define ADDR_START_BIT 12
 
 /* Updates the 'owner' thread's page table entry for virtual address 'upage'
    to have a present bit of 0 and stores the specified swap slot value in the
@@ -11,17 +6,7 @@
 void
 page_set_swap (struct thread *owner, void *upage, size_t swap_slot)
 {
-   uint32_t *pte = lookup_page (owner->pagedir, upage, false);
 
-   /* Store the provided swap slot in the address bits of the page table
-      entry, truncating excess bits. */
-   *pte |= (1 << SWAP_FLAG_BIT);
-   uint32_t swap_slot_bits = (swap_slot << ADDR_START_BIT) & PTE_ADDR;
-   *pte = (*pte & PTE_FLAGS) | swap_slot_bits;
-
-   /* Mark page as 'not present' and flag the page directory as having
-      been modified. */
-   pagedir_clear_page (owner->pagedir, upage);
 }
 
 /* Given that the page with user address 'upage' owned by 'owner' is flagged
@@ -30,12 +15,6 @@ page_set_swap (struct thread *owner, void *upage, size_t swap_slot)
 size_t
 page_get_swap (struct thread *owner, void *upage)
 {
-   uint32_t *pte = lookup_page (owner->pagedir, upage, false);
 
-   ASSERT ((*pte & PTE_P) == 0);
-   ASSERT ((*pte & (1 << SWAP_FLAG_BIT)) != 0);
-
-   /* Masks the address bits and returns truncated value. */
-   return ((*pte & PTE_ADDR) >> ADDR_START_BIT);
 }
 

src/vm/stackgrowth.c

@@ -1,59 +0,0 @@
-#include <stdio.h>
-#include "stackgrowth.h"
-#include "frame.h"
-#include "threads/palloc.h"
-#include "threads/thread.h"
-#include "threads/vaddr.h"
-#include "userprog/pagedir.h"
-
-#define MAX_STACK_ACCESS_DIST 32
-
-static bool is_stack_fault (const void *addr, const void *esp);
-static bool grow_stack (const void *addr);
-
-/* Determine whether a particular page fault occured due to a stack
-   access below the stack pointer that should induce stack growth, and
-   if so grow the stack by a single page (capped at MAX_STACK_SIZE). */
-bool
-handle_stack_fault (const void *ptr, const void *esp)
-{
-  return is_stack_fault (ptr, esp) && grow_stack (ptr);
-}
-
-/* Determines whether a particular page fault appears to be caused by
-   a stack access that should induce dynamic stack growth. Stack size
-   is capped at MAX_STACK_SIZE. */
-static bool
-is_stack_fault (const void *addr, const void *esp)
-{
-  return ((uint32_t*)addr >= ((uint32_t*)esp - MAX_STACK_ACCESS_DIST) &&
-          ((PHYS_BASE - pg_round_down (addr)) <= MAX_STACK_SIZE));
-}
-
-/* Grows the stack of the process running inside the current thread by a single
-   page given a user virtual address inside of the page wherein the new section
-   of the stack should be allocated. */
-static bool
-grow_stack (const void *addr)
-{
-  struct thread *t = thread_current ();
-  void *last_page = pg_round_down (addr);
-
-  /* This function should only be called when dealing with a faulting stack
-     access that induces stack growth, so the provided address shouldn't be
-     present in a page within the current thread's page directory. */
-  ASSERT (pagedir_get_page (t->pagedir, last_page) == NULL);
-
-  uint8_t *new_page = frame_alloc (PAL_ZERO, last_page, t);
-  if (new_page == NULL)
-    return false;
-
-  if (!pagedir_set_page (t->pagedir, last_page, new_page, true))
-  {
-    frame_free (new_page);
-    return false;
-  }
-
-  return true;
-}
-

src/vm/stackgrowth.h

@@ -1,10 +0,0 @@
-#ifndef VM_GROWSTACK_H
-#define VM_GROWSTACK_H
-
-#include <stdio.h>
-
-#define MAX_STACK_SIZE 8388608 // (8MB)
-
-bool handle_stack_fault (const void *ptr, const void *esp);
-
-#endif /* vm/frame.h */